The present invention relates to a coating composition which comprises:
(A) at least one component which contains hydroxy groups, and PA1 (B) at least one crosslinking agent, characterized in that aromatic mono- and/or polycarboxylic acid and/or an anhydride of an aromatic polycarboxylic acid are added to component (A) after its preparation or to the coating composition. PA1 (A1) from 20 to 60% by weight, preferably from 30 to 50% by weight, of at least one polyester, and PA1 (A2) from 40 to 80% by weight, preferably from 50 to 70% by weight, at least one polyacrylate resin which contains hydroxyl groups and has been prepared at least partially in the presence of components (A1). PA1 p1) polycarboxylic acids or their esterifiable derivatives, together if desired with monocarboxylic acids, PA1 p2) polyols, together if desired with monools, PA1 p3) if desired, other modifying components, and PA1 p4) if desired, a component which is capable of reaction with the reaction product of (p1), (p2) and, if appropriate, (p3). PA1 (P.sub.12)one or more monomers selected from the group of 3-hydroxy-n-propyl acrylate and/or 3-hydroxy-n-propyl methacrylate and/or 2-hydroxy-n-propyl acryalte and/or 2-ydroxy-n-propyl methacrylate;
The present invention also relates to processes for the production of a protective and/or decorative coating on a substrate surface and to the use of the coating composition in the area of automotive refinishing.
DE-A-40 24 204 has already disclosed coating compositions which contain, as binder, a polyacrylate resin which contains hydroxyl groups and has been prepared in the presence of a polyester which contains hydroxyl groups. However, especially when these coating compositions are applied at low temperatures, from about 8 to 12.degree. C., the masking resistance and solvent resistance of the resulting coatings is in need of improvement.
In the area of the finishing of large-size vehicles, for example the finishing of goods-vehicle bodies, the masking resistance of the resulting coatings is of particular importance. This is because large-size vehicles are commonly provided with written characters, whose application requires the adjacent area to be masked off. If the masking resistance is inadequate, the marks must be removed by hand, by laborious sanding and polishing, which entails a considerable financial outlay.
Furthermore, the coating compositions must also cure as rapidly as possible, in order to avoid excessive standing times between the individual operations in the coating plant. These coating compositions must also, of course, possess good application properties and lead to coatings having good mechanical properties.
In addition, DE-A-31 33 769 discloses that the curing rate of one-component polyurethane coating compositions based on amines and on compounds containing isocyanate groups can be increased by the addition of benzoic acid. These coating compositions known from DE-A-31 33 769 differ from the coating compositions according to the invention in that no description is given of coating compositions based on polymers containing hydroxyl groups and on crosslinking agents containing isocyanate groups.
Futhermore, U.S. Pat. No. 3,897,396 discloses that the curing rate of molding compositions based on polyurethane-ureas can be increased by the addition of alkyl- or alkozybenzoic acid, without thereby shortening the pot life.
These compositions known from U.S. Pat. No. 3,897,396 differ from the coating compositions according to the invention in that U.S. Pat. No. 3,897,396 describes molding compositions rather than coating compositions. Furthermore, these molding compositions known from U.S. Pat. No. 3,897,396 contain binders comprising prepolymers which contain isocyanate groups and are based on the reaction product of a polyetherpolyol, polyesterpolyol or hydrocarbonpolyol with isocyanate and a crosslinking agent comprising polyamines. Compositions based on acrylate copolymers containing hydroxyl groups and on compounds containing isocyanate groups, on the other hand, are not described in U.S. Pat. No. 3,897,396.
Finally, German Patent Application P 44 07 409.3, which is not a prior publication, discloses coating compositions containing a polyacrylate resin, which contains hydroxyl groups and is based on hydroxy-n-butyl acrylate, and a crosslinking agent. The preparation of the polyacrylate resin in the presence of a polyester resin, however, is not described in this application.